1. Field of the Invention
The present invention relates to a traffic output suppression apparatus and a method for recognizing a state of an asynchronous transfer mode (referred to hereinafter as ATM) network node and preventing congestion due to a variation of the input traffic to the ATM network node in accordance with the recognized result, the traffic output suppression apparatus being disposed in a user-network interface unit connected to the ATM network node.
2. Description of the Prior Art
Conventional congestion control methods include a prevention control method such as a connection accept control (CAC) method or a user parameter control (UPC) method, and a reaction control method such as an explicit congestion notification (ECN) method. The prevention control method utilizes fixed traffic parameters which are previously adjusted for the observance of a traffic amount negotiated between an ATM network and the user. The reaction control method utilizes a congestion notification signal so that no further bad effect can be exerted on adjacent ATM network nodes or terminals after congestion has occurred.
However, although the conventional prevention control method enables ATM virtual connections to observe the negotiated traffic amount, the congestion occurrence probability is still present under the control using the fixed traffic parameters, in the case where traffic after a statistical multiplexing operation is performed in a user-network interface means is directly transferred to the adjacent ATM network node- Namely, in this case, the control using the fixed traffic parameters cannot perfectly cope with a variation in the amount of traffic due to the setting and release of the ATM virtual connections and an unpredictable variation of the traffic stream due to a statistical characteristic. On the other hand, the conventional reaction control method has nothing but signifying emergency means after the congestion occurs in the ATM network node. Further, a longer delay time required in the transfer of the congestion notification signal makes the protection of user's important information more difficult.